One proposed structure of the heat exchanger has multiple tubes arranged to make circulation of a refrigerant between a refrigerant inlet tank and a refrigerant outlet tank and thereby perform heat exchange with the outside air (see, for example, Japanese Patent Laid-Open No. 2001-167782). In the heat exchanger of this prior art structure, as the refrigerant introduced into the inlet tank flows in the multiple tubes and reaches the outlet tank, the refrigerant is cooled down by heat exchange with the outside air flowing between the multiple tubes in a direction substantially perpendicular to the multiple tubes. Cooling fins are provided between the multiple tubes to enhance the efficiency of heat exchange.
Another proposed structure of the heat exchanger has multiple small-diameter tubes arranged to make circulation of a refrigerant between two headers formed as an inlet and an outlet of a refrigerant and thereby perform heat exchange with the outside air (see, for example, Japanese Patent Laid-Open No. 2004-218969). In the heat exchanger of this prior art structure, as the refrigerant flows in and between the multiple small-diameter tubes, the refrigerant is cooled down by heat exchange with the outside air.
Still another proposed structure of the heat exchanger has multiple flattened hollow tubes of a flattened cross section, in order to increase an effective area of heat transfer. This prior art heat exchanger is constructed as a finless heat exchanger with no cooling fans, in order to lower a potential pressure loss of a fluid flowing between the flattened tubes and attain size reduction of the heat exchanger.